1. Industrial Field of the Invention
The present invention relates to a bearing unit for supporting a main shaft of a machine tool or a rotation shaft of a motor, in a grease lubricated condition.
2. Description of the Prior Art
In angular contact ball bearings, cylindrical roller bearings or tapered roller bearings for supporting a shaft which rotates at high speed such as a main shaft of a high speed machine, the prevention of contamination with foreign matter is generally effected by providing a sealing device such as a labyrinth seal on the side of the apparatus to be used, with no sealing device provided for the bearing. On the other hand, a bearing has also been developed in which leakage of internally filled grease and contamination with foreign matter are prevented, by having a built in sealing device. However in order to install such a sealing device, special specifications such as a wider width are required. Furthermore, heat release effectiveness is reduced, and so grease life tends to be short.
In particular in the case of machine tools, due to problems with heat which has an affect on machining accuracy, the use of contact type seals is avoided, which causes difficulties. Consequently, it is common to provide multi-step labyrinth seals.
From this view point, angular contact ball bearings, cylindrical roller bearings or tapered roller bearings for supporting a main shaft of a machine tool or a rotation shaft of a motor which rotate at high speed, are of the open type with good heat dissipation. It is thus necessary to consider the influence in the case where cutting fluid, foreign matter or the like during machining passes through a sealing device provided on the shaft or housing, and infiltrates into the bearing interior. Furthermore, since the leakage of grease from the bearing interior occurs easily, the lubricated condition of the bearing deteriorates.
Therefore, in order to prevent the infiltration of foreign matter, a sealing device such as a multi-step labyrinth seal is provided on the shaft or the housing. Furthermore, prevention of infiltration is effected mechanically with air purge using the flow of air. Alternatively, this is also effected by providing a non-contact type seal in the bearing itself. However, in this case, there is a problem in that foreign matter infiltrates in through the gap of several hundred microns to several millimeters inherent with non-contact type seals such as labyrinth seals, and grease leaks out, so that the sealing effect is insufficient.
There is also a case where such a problem can be solved by a bearing in which a contact type sealing device is provided. However, as mentioned above, by providing such a sealing device, the heat dissipation effect is reduced. Moreover, in cases for example where a combined bearing unit is used, a pressure difference between the inside and outside occurs with temperature change of the bearing interior, and when the interior of the combined bearing unit becomes a low pressure, cutting fluid or foreign matter is drawn in from the outside, and the sealing effect cannot be maintained. In the case where cutting fluid or foreign matter enters the bearing interior or grease leaks out, bearing failing at an early stage is likely. In order to prevent this, maintenance over a relatively short cycle is necessary. Hence running costs are increased.
An objective of the present invention, taking into consideration such problems, is to provide a bearing unit which can effectively suppress the infiltration of foreign matter to inside the bearing, and which can effectively suppress the leakage of grease.
Another object of the present invention is to provide a bearing unit which comprises; a bearing having an inner ring, an outer ring and at least one row of rolling elements arranged so as to be freely rotatable between the inner ring and the outer ring, and a sealing device arranged on axially either side of the bearing, wherein the sealing device has a fixed ring spacer, a rotating ring spacer, and a non-contact seal section attached to one of the fixed ring spacer and the rotating ring spacer and extending towards the other to maintain in a non-contact condition with respect to the other.